<?php

/**
 * @file
 * Drupal database update API.
 *
 * This file contains functions to perform database updates for a Drupal
 * installation. It is included and used extensively by update.php.
 */

/**
 * Minimum schema version of Drupal 6 required for upgrade to Drupal 7.
 *
 * Upgrades from Drupal 6 to Drupal 7 require that Drupal 6 be running
 * the most recent version, or the upgrade could fail. We can't easily
 * check the Drupal 6 version once the update process has begun, so instead
 * we check the schema version of system.module in the system table.
 */
define('REQUIRED_D6_SCHEMA_VERSION', '6055');

/**
 * Disable any items in the {system} table that are not core compatible.
 */
function update_fix_compatibility() {
	$incompatible = array();
	$result = db_query("SELECT name, type, status FROM {system} WHERE status = 1 AND type IN ('module','theme')");
	foreach ($result as $row) {
		if (update_check_incompatibility($row->name, $row->type)) {
			$incompatible[] = $row->name;
		}
	}
	if (!empty($incompatible)) {
		db_update('system')
		->fields(array('status' => 0))
		->condition('name', $incompatible, 'IN')
		->execute();
	}
}

/**
 * Helper function to test compatibility of a module or theme.
 */
function update_check_incompatibility($name, $type = 'module') {
	static $themes, $modules;

	// Store values of expensive functions for future use.
	if (empty($themes) || empty($modules)) {
		// We need to do a full rebuild here to make sure the database reflects any
		// code changes that were made in the filesystem before the update script
		// was initiated.
		$themes = system_rebuild_theme_data();
		$modules = system_rebuild_module_data();
	}

	if ($type == 'module' && isset($modules[$name])) {
		$file = $modules[$name];
	}
	elseif ($type == 'theme' && isset($themes[$name])) {
		$file = $themes[$name];
	}
	if (!isset($file)
			|| !isset($file->info['core'])
			|| $file->info['core'] != DRUPAL_CORE_COMPATIBILITY
			|| version_compare(phpversion(), $file->info['php']) < 0) {
		return TRUE;
	}
	return FALSE;
}

/**
 * Performs extra steps required to bootstrap when using a Drupal 6 database.
 *
 * Users who still have a Drupal 6 database (and are in the process of
 * updating to Drupal 7) need extra help before a full bootstrap can be
 * achieved. This function does the necessary preliminary work that allows
 * the bootstrap to be successful.
 *
 * No access check has been performed when this function is called, so no
 * irreversible changes to the database are made here.
 */
function update_prepare_d7_bootstrap() {
	// Allow the bootstrap to proceed even if a Drupal 6 settings.php file is
	// still being used.
	include_once DRUPAL_ROOT . '/includes/install.inc';
	drupal_bootstrap(DRUPAL_BOOTSTRAP_CONFIGURATION);
	global $databases, $db_url, $db_prefix, $update_rewrite_settings;
	if (empty($databases) && !empty($db_url)) {
		$databases = update_parse_db_url($db_url, $db_prefix);
		// Record the fact that the settings.php file will need to be rewritten.
		$update_rewrite_settings = TRUE;
		$settings_file = conf_path() . '/settings.php';
		$writable = drupal_verify_install_file($settings_file, FILE_EXIST|FILE_READABLE|FILE_WRITABLE);
		$requirements = array(
				'settings file' => array(
						'title' => 'Settings file',
						'value' => $writable ? 'The settings file is writable.' : 'The settings file is not writable.',
						'severity' => $writable ? REQUIREMENT_OK : REQUIREMENT_ERROR,
						'description' => $writable ? '' : 'Drupal requires write permissions to <em>' . $settings_file . '</em> during the update process. If you are unsure how to grant file permissions, consult the <a href="http://drupal.org/server-permissions">online handbook</a>.',
				),
		);
		update_extra_requirements($requirements);
	}

	// The new {blocked_ips} table is used in Drupal 7 to store a list of
	// banned IP addresses. If this table doesn't exist then we are still
	// running on a Drupal 6 database, so we suppress the unavoidable errors
	// that occur by creating a static list.
	$GLOBALS['conf']['blocked_ips'] = array();

	// Check that PDO is available and that the correct PDO database driver is
	// loaded. Bootstrapping to DRUPAL_BOOTSTRAP_DATABASE will result in a fatal
	// error otherwise.
	$message = '';
	$pdo_link = 'http://drupal.org/requirements/pdo';
	// Check that PDO is loaded.
	if (!extension_loaded('pdo')) {
		$message = '<h2>PDO is required!</h2><p>Drupal 7 requires PHP ' . DRUPAL_MINIMUM_PHP . ' or higher with the PHP Data Objects (PDO) extension enabled.</p>';
	}
	// The PDO::ATTR_DEFAULT_FETCH_MODE constant is not available in the PECL
	// version of PDO.
	elseif (!defined('PDO::ATTR_DEFAULT_FETCH_MODE')) {
		$message = '<h2>The wrong version of PDO is installed!</h2><p>Drupal 7 requires the PHP Data Objects (PDO) extension from PHP core to be enabled. This system has the older PECL version installed.';
		$pdo_link = 'http://drupal.org/requirements/pdo#pecl';
	}
	// Check that the correct driver is loaded for the database being updated.
	// If we have no driver information (for example, if someone tried to create
	// the Drupal 7 $databases array themselves but did not do it correctly),
	// this message will be confusing, so do not perform the check; instead, just
	// let the database connection fail in the code that follows.
	elseif (isset($databases['default']['default']['driver']) && !in_array($databases['default']['default']['driver'], PDO::getAvailableDrivers())) {
		$message = '<h2>A PDO database driver is required!</h2><p>You need to enable the PDO_' . strtoupper($databases['default']['default']['driver']) . ' database driver for PHP ' . DRUPAL_MINIMUM_PHP . ' or higher so that Drupal 7 can access the database.</p>';
	}
	if ($message) {
		print $message . '<p>See the <a href="' . $pdo_link . '">system requirements page</a> for more information.</p>';
		exit();
	}

	// Allow the database system to work even if the registry has not been
	// created yet.
	drupal_bootstrap(DRUPAL_BOOTSTRAP_DATABASE);

	// If the site has not updated to Drupal 7 yet, check to make sure that it is
	// running an up-to-date version of Drupal 6 before proceeding. Note this has
	// to happen AFTER the database bootstraps because of
	// drupal_get_installed_schema_version().
	$system_schema = drupal_get_installed_schema_version('system');
	if ($system_schema < 7000) {
		$has_required_schema = $system_schema >= REQUIRED_D6_SCHEMA_VERSION;
		$requirements = array(
				'drupal 6 version' => array(
						'title' => 'Drupal 6 version',
						'value' => $has_required_schema ? 'You are running a current version of Drupal 6.' : 'You are not running a current version of Drupal 6',
						'severity' => $has_required_schema ? REQUIREMENT_OK : REQUIREMENT_ERROR,
						'description' => $has_required_schema ? '' : 'Please update your Drupal 6 installation to the most recent version before attempting to upgrade to Drupal 7',
				),
		);

		// Make sure that the database environment is properly set up.
		try {
			db_run_tasks(db_driver());
		}
		catch (DatabaseTaskException $e) {
			$requirements['database tasks'] = array(
					'title' => 'Database environment',
					'value' => 'There is a problem with your database environment',
					'severity' => REQUIREMENT_ERROR,
					'description' => $e->getMessage(),
			);
		}

		update_extra_requirements($requirements);

		// Allow a D6 session to work, since the upgrade has not been performed yet.
		$d6_session_name = update_get_d6_session_name();
		if (!empty($_COOKIE[$d6_session_name])) {
			// Set the current sid to the one found in the D6 cookie.
			$sid = $_COOKIE[$d6_session_name];
			$_COOKIE[session_name()] = $sid;
			session_id($sid);
		}

		// Upgrading from D6 to D7.{0,1,2,3,4,8,...} is different than upgrading
		// from D6 to D7.{5,6,7} which should be considered broken. To be able to
		// properly handle this difference in node_update_7012 we need to keep track
		// of whether a D6 > D7 upgrade or a D7 > D7 update is running.
		// Since variable_set() is not available here, the D6 status is being saved
		// in a local variable to be able to store it later.
		$update_d6 = TRUE;
	}

	// Create the registry tables.
	if (!db_table_exists('registry')) {
		$schema['registry'] = array(
				'fields' => array(
						'name'   => array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''),
						'type'   => array('type' => 'varchar', 'length' => 9, 'not null' => TRUE, 'default' => ''),
						'filename'   => array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''),
						'module'   => array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''),
						'weight'   => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
				),
				'primary key' => array('name', 'type'),
				'indexes' => array(
						'hook' => array('type', 'weight', 'module'),
				),
		);
		db_create_table('registry', $schema['registry']);
	}
	if (!db_table_exists('registry_file')) {
		$schema['registry_file'] = array(
				'fields' => array(
						'filename'   => array('type' => 'varchar', 'length' => 255, 'not null' => TRUE),
						'hash'   => array('type' => 'varchar', 'length' => 64, 'not null' => TRUE),
				),
				'primary key' => array('filename'),
		);
		db_create_table('registry_file', $schema['registry_file']);
	}

	// Older versions of Drupal 6 do not include the semaphore table, which is
	// required to bootstrap, so we add it now so that we can bootstrap and
	// provide a reasonable error message.
	if (!db_table_exists('semaphore')) {
		$semaphore = array(
				'description' => 'Table for holding semaphores, locks, flags, etc. that cannot be stored as Drupal variables since they must not be cached.',
				'fields' => array(
						'name' => array(
								'description' => 'Primary Key: Unique name.',
								'type' => 'varchar',
								'length' => 255,
								'not null' => TRUE,
								'default' => ''
						),
						'value' => array(
								'description' => 'A value for the semaphore.',
								'type' => 'varchar',
								'length' => 255,
								'not null' => TRUE,
								'default' => ''
						),
						'expire' => array(
								'description' => 'A Unix timestamp with microseconds indicating when the semaphore should expire.',
								'type' => 'float',
								'size' => 'big',
								'not null' => TRUE
						),
				),
				'indexes' => array(
						'value' => array('value'),
						'expire' => array('expire'),
				),
				'primary key' => array('name'),
		);
		db_create_table('semaphore', $semaphore);
	}

	// The new cache_bootstrap bin is required to bootstrap to
	// DRUPAL_BOOTSTRAP_SESSION, so create it here rather than in
	// update_fix_d7_requirements().
	if (!db_table_exists('cache_bootstrap')) {
		$cache_bootstrap = array(
				'description' => 'Cache table for data required to bootstrap Drupal, may be routed to a shared memory cache.',
				'fields' => array(
						'cid' => array(
								'description' => 'Primary Key: Unique cache ID.',
								'type' => 'varchar',
								'length' => 255,
								'not null' => TRUE,
								'default' => '',
						),
						'data' => array(
								'description' => 'A collection of data to cache.',
								'type' => 'blob',
								'not null' => FALSE,
								'size' => 'big',
						),
						'expire' => array(
								'description' => 'A Unix timestamp indicating when the cache entry should expire, or 0 for never.',
								'type' => 'int',
								'not null' => TRUE,
								'default' => 0,
						),
						'created' => array(
								'description' => 'A Unix timestamp indicating when the cache entry was created.',
								'type' => 'int',
								'not null' => TRUE,
								'default' => 0,
						),
						'serialized' => array(
								'description' => 'A flag to indicate whether content is serialized (1) or not (0).',
								'type' => 'int',
								'size' => 'small',
								'not null' => TRUE,
								'default' => 0,
						),
				),
				'indexes' => array(
						'expire' => array('expire'),
				),
				'primary key' => array('cid'),
		);
		db_create_table('cache_bootstrap', $cache_bootstrap);
	}

	// Set a valid timezone for 6 -> 7 upgrade process.
	drupal_bootstrap(DRUPAL_BOOTSTRAP_VARIABLES);
	$timezone_offset = variable_get('date_default_timezone', 0);
	if (is_numeric($timezone_offset)) {
		// Save the original offset.
		variable_set('date_temporary_timezone', $timezone_offset);
		// Set the timezone for this request only.
		$GLOBALS['conf']['date_default_timezone'] = 'UTC';
	}

	// This allows update functions to tell if an upgrade from D6 is running.
	if (!empty($update_d6)) {
		variable_set('update_d6', TRUE);
	}
}

/**
 * A helper function that modules can use to assist with the transformation
 * from numeric block deltas to string block deltas during the 6.x -> 7.x
 * upgrade.
 *
 * @todo This function should be removed in 8.x.
 *
 * @param $sandbox
 *   An array holding data for the batch process.
 * @param $renamed_deltas
 *   An associative array.  Keys are module names, values an associative array
 *   mapping the old block deltas to the new block deltas for the module.
 *   Example:
 *   @code
 *     $renamed_deltas = array(
 *       'mymodule' =>
 *         array(
 *           0 => 'mymodule-block-1',
 *           1 => 'mymodule-block-2',
 *         ),
 *     );
 *   @endcode
 * @param $moved_deltas
 *   An associative array. Keys are source module names, values an associative
 *   array mapping the (possibly renamed) block name to the new module name.
 *   Example:
 *   @code
 *     $moved_deltas = array(
 *       'user' =>
 *         array(
 *           'navigation' => 'system',
 *         ),
 *     );
 *   @endcode
 */
function update_fix_d7_block_deltas(&$sandbox, $renamed_deltas, $moved_deltas) {
	// Loop through each block and make changes to the block tables.
	// Only run this the first time through the batch update.
	if (!isset($sandbox['progress'])) {
		// Determine whether to use the old or new block table names.
		$block_tables = db_table_exists('blocks') ? array('blocks', 'blocks_roles') : array('block', 'block_role');
		foreach ($block_tables as $table) {
			foreach ($renamed_deltas as $module => $deltas) {
				foreach ($deltas as $old_delta => $new_delta) {
					// Only do the update if the old block actually exists.
					$block_exists = db_query("SELECT COUNT(*) FROM {" . $table . "} WHERE module = :module AND delta = :delta", array(
							':module' => $module,
							':delta' => $old_delta,
					))
					->fetchField();
					if ($block_exists) {
						// Delete any existing blocks with the new module+delta.
						db_delete($table)
						->condition('module', $module)
						->condition('delta', $new_delta)
						->execute();
						// Rename the old block to the new module+delta.
						db_update($table)
						->fields(array('delta' => $new_delta))
						->condition('module', $module)
						->condition('delta', $old_delta)
						->execute();
					}
				}
			}
			foreach ($moved_deltas as $old_module => $deltas) {
				foreach ($deltas as $delta => $new_module) {
					// Only do the update if the old block actually exists.
					$block_exists = db_query("SELECT COUNT(*) FROM {" . $table . "} WHERE module = :module AND delta = :delta", array(
							':module' => $old_module,
							':delta' => $delta,
					))
					->fetchField();
					if ($block_exists) {
						// Delete any existing blocks with the new module+delta.
						db_delete($table)
						->condition('module', $new_module)
						->condition('delta', $delta)
						->execute();
						// Rename the old block to the new module+delta.
						db_update($table)
						->fields(array('module' => $new_module))
						->condition('module', $old_module)
						->condition('delta', $delta)
						->execute();
					}
				}
			}
		}

		// Initialize batch update information.
		$sandbox['progress'] = 0;
		$sandbox['last_user_processed'] = -1;
		$sandbox['max'] = db_query("SELECT COUNT(*) FROM {users} WHERE data IS NOT NULL")->fetchField();
	}
	// Now do the batch update of the user-specific block visibility settings.
	$limit = 100;
	$result = db_select('users', 'u')
	->fields('u', array('uid', 'data'))
	->condition('uid', $sandbox['last_user_processed'], '>')
	->orderBy('uid', 'ASC')
	->where('data IS NOT NULL')
	->range(0, $limit)
	->execute();
	foreach ($result as $row) {
		$data = unserialize($row->data);
		$user_needs_update = FALSE;
		foreach ($renamed_deltas as $module => $deltas) {
			foreach ($deltas as $old_delta => $new_delta) {
				if (isset($data['block'][$module][$old_delta])) {
					// Transfer the old block visibility settings to the newly-renamed
					// block, and mark this user for a database update.
					$data['block'][$module][$new_delta] = $data['block'][$module][$old_delta];
					unset($data['block'][$module][$old_delta]);
					$user_needs_update = TRUE;
				}
			}
		}
		foreach ($moved_deltas as $old_module => $deltas) {
			foreach ($deltas as $delta => $new_module) {
				if (isset($data['block'][$old_module][$delta])) {
					// Transfer the old block visibility settings to the moved
					// block, and mark this user for a database update.
					$data['block'][$new_module][$delta] = $data['block'][$old_module][$delta];
					unset($data['block'][$old_module][$delta]);
					$user_needs_update = TRUE;
				}
			}
		}
		// Update the current user.
		if ($user_needs_update) {
			db_update('users')
			->fields(array('data' => serialize($data)))
			->condition('uid', $row->uid)
			->execute();
		}
		// Update our progress information for the batch update.
		$sandbox['progress']++;
		$sandbox['last_user_processed'] = $row->uid;
	}
	// Indicate our current progress to the batch update system.
	if ($sandbox['progress'] < $sandbox['max']) {
		$sandbox['#finished'] = $sandbox['progress'] / $sandbox['max'];
	}
}

/**
 * Perform Drupal 6.x to 7.x updates that are required for update.php
 * to function properly.
 *
 * This function runs when update.php is run the first time for 7.x,
 * even before updates are selected or performed. It is important
 * that if updates are not ultimately performed that no changes are
 * made which make it impossible to continue using the prior version.
 */
function update_fix_d7_requirements() {
	global $conf;

	// Rewrite the settings.php file if necessary, see
	// update_prepare_d7_bootstrap().
	global $update_rewrite_settings, $db_url, $db_prefix;
	if (!empty($update_rewrite_settings)) {
		$databases = update_parse_db_url($db_url, $db_prefix);
		$salt = drupal_hash_base64(drupal_random_bytes(55));
		file_put_contents(conf_path() . '/settings.php', "\n" . '$databases = ' . var_export($databases, TRUE) . ";\n\$drupal_hash_salt = '$salt';", FILE_APPEND);
	}
	if (drupal_get_installed_schema_version('system') < 7000 && !variable_get('update_d7_requirements', FALSE)) {
		// Change 6.x system table field values to 7.x equivalent.
		// Change field values.
		db_change_field('system', 'schema_version', 'schema_version', array(
				'type' => 'int',
				'size' => 'small',
				'not null' => TRUE,
				'default' => -1)
		);
		db_change_field('system', 'status', 'status', array(
				'type' => 'int', 'not null' => TRUE, 'default' => 0));
		db_change_field('system', 'weight', 'weight', array(
				'type' => 'int', 'not null' => TRUE, 'default' => 0));
		db_change_field('system', 'bootstrap', 'bootstrap', array(
				'type' => 'int', 'not null' => TRUE, 'default' => 0));
		// Drop and recreate 6.x indexes.
		db_drop_index('system', 'bootstrap');
		db_add_index('system', 'bootstrap', array(
				'status', 'bootstrap', array('type', 12), 'weight', 'name'));

		db_drop_index('system' ,'modules');
		db_add_index('system', 'modules', array(array(
				'type', 12), 'status', 'weight', 'name'));

		db_drop_index('system', 'type_name');
		db_add_index('system', 'type_name', array(array('type', 12), 'name'));
		// Add 7.x indexes.
		db_add_index('system', 'system_list', array('weight', 'name'));

		// Add the cache_path table.
		if (db_table_exists('cache_path')) {
			db_drop_table('cache_path');
		}
		require_once('./modules/system/system.install');
		$schema['cache_path'] = system_schema_cache_7054();
		$schema['cache_path']['description'] = 'Cache table used for path alias lookups.';
		db_create_table('cache_path', $schema['cache_path']);

		// system_update_7042() renames columns, but these are needed to bootstrap.
		// Add empty columns for now.
		db_add_field('url_alias', 'source', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''));
		db_add_field('url_alias', 'alias', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''));

		// Add new columns to {menu_router}.
		db_add_field('menu_router', 'delivery_callback', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''));
		db_add_field('menu_router', 'context', array(
				'description' => 'Only for local tasks (tabs) - the context of a local task to control its placement.',
				'type' => 'int',
				'not null' => TRUE,
				'default' => 0,
		));
		db_drop_index('menu_router', 'tab_parent');
		db_add_index('menu_router', 'tab_parent', array(array('tab_parent', 64), 'weight', 'title'));
		db_add_field('menu_router', 'theme_callback', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''));
		db_add_field('menu_router', 'theme_arguments', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''));

		// Add the role_permission table.
		$schema['role_permission'] = array(
				'fields' => array(
						'rid' => array(
								'type' => 'int',
								'unsigned' => TRUE,
								'not null' => TRUE,
						),
						'permission' => array(
								'type' => 'varchar',
								'length' => 128,
								'not null' => TRUE,
								'default' => '',
						),
				),
				'primary key' => array('rid', 'permission'),
				'indexes' => array(
						'permission' => array('permission'),
				),
		);
		db_create_table('role_permission', $schema['role_permission']);

		// Drops and recreates semaphore value index.
		db_drop_index('semaphore', 'value');
		db_add_index('semaphore', 'value', array('value'));

		$schema['date_format_type'] = array(
				'description' => 'Stores configured date format types.',
				'fields' => array(
						'type' => array(
								'description' => 'The date format type, e.g. medium.',
								'type' => 'varchar',
								'length' => 64,
								'not null' => TRUE,
						),
						'title' => array(
								'description' => 'The human readable name of the format type.',
								'type' => 'varchar',
								'length' => 255,
								'not null' => TRUE,
						),
						'locked' => array(
								'description' => 'Whether or not this is a system provided format.',
								'type' => 'int',
								'size' => 'tiny',
								'default' => 0,
								'not null' => TRUE,
						),
				),
				'primary key' => array('type'),
		);

		$schema['date_formats'] = array(
				'description' => 'Stores configured date formats.',
				'fields' => array(
						'dfid' => array(
								'description' => 'The date format identifier.',
								'type' => 'serial',
								'not null' => TRUE,
								'unsigned' => TRUE,
						),
						'format' => array(
								'description' => 'The date format string.',
								'type' => 'varchar',
								'length' => 100,
								'not null' => TRUE,
						),
						'type' => array(
								'description' => 'The date format type, e.g. medium.',
								'type' => 'varchar',
								'length' => 64,
								'not null' => TRUE,
						),
						'locked' => array(
								'description' => 'Whether or not this format can be modified.',
								'type' => 'int',
								'size' => 'tiny',
								'default' => 0,
								'not null' => TRUE,
						),
				),
				'primary key' => array('dfid'),
				'unique keys' => array('formats' => array('format', 'type')),
		);

		$schema['date_format_locale'] = array(
				'description' => 'Stores configured date formats for each locale.',
				'fields' => array(
						'format' => array(
								'description' => 'The date format string.',
								'type' => 'varchar',
								'length' => 100,
								'not null' => TRUE,
						),
						'type' => array(
								'description' => 'The date format type, e.g. medium.',
								'type' => 'varchar',
								'length' => 64,
								'not null' => TRUE,
						),
						'language' => array(
								'description' => 'A {languages}.language for this format to be used with.',
								'type' => 'varchar',
								'length' => 12,
								'not null' => TRUE,
						),
				),
				'primary key' => array('type', 'language'),
		);

		db_create_table('date_format_type', $schema['date_format_type']);
		// Sites that have the Drupal 6 Date module installed already have the
		// following tables.
		if (db_table_exists('date_formats')) {
			db_rename_table('date_formats', 'd6_date_formats');
		}
		db_create_table('date_formats', $schema['date_formats']);
		if (db_table_exists('date_format_locale')) {
			db_rename_table('date_format_locale', 'd6_date_format_locale');
		}
		db_create_table('date_format_locale', $schema['date_format_locale']);

		// Add the queue table.
		$schema['queue'] = array(
				'description' => 'Stores items in queues.',
				'fields' => array(
						'item_id' => array(
								'type' => 'serial',
								'unsigned' => TRUE,
								'not null' => TRUE,
								'description' => 'Primary Key: Unique item ID.',
						),
						'name' => array(
								'type' => 'varchar',
								'length' => 255,
								'not null' => TRUE,
								'default' => '',
								'description' => 'The queue name.',
						),
						'data' => array(
								'type' => 'blob',
								'not null' => FALSE,
								'size' => 'big',
								'serialize' => TRUE,
								'description' => 'The arbitrary data for the item.',
						),
						'expire' => array(
								'type' => 'int',
								'not null' => TRUE,
								'default' => 0,
								'description' => 'Timestamp when the claim lease expires on the item.',
						),
						'created' => array(
								'type' => 'int',
								'not null' => TRUE,
								'default' => 0,
								'description' => 'Timestamp when the item was created.',
						),
				),
				'primary key' => array('item_id'),
				'indexes' => array(
						'name_created' => array('name', 'created'),
						'expire' => array('expire'),
				),
		);
		// Check for queue table that may remain from D5 or D6, if found
		//drop it.
		if (db_table_exists('queue')) {
			db_drop_table('queue');
		}

		db_create_table('queue', $schema['queue']);

		// Create the sequences table.
		$schema['sequences'] = array(
				'description' => 'Stores IDs.',
				'fields' => array(
						'value' => array(
								'description' => 'The value of the sequence.',
								'type' => 'serial',
								'unsigned' => TRUE,
								'not null' => TRUE,
						),
				),
				'primary key' => array('value'),
		);
		// Check for sequences table that may remain from D5 or D6, if found
		//drop it.
		if (db_table_exists('sequences')) {
			db_drop_table('sequences');
		}
		db_create_table('sequences', $schema['sequences']);
		// Initialize the table with the maximum current increment of the tables
		// that will rely on it for their ids.
		$max_aid = db_query('SELECT MAX(aid) FROM {actions_aid}')->fetchField();
		$max_uid = db_query('SELECT MAX(uid) FROM {users}')->fetchField();
		$max_batch_id = db_query('SELECT MAX(bid) FROM {batch}')->fetchField();
		db_insert('sequences')->fields(array('value' => max($max_aid, $max_uid, $max_batch_id)))->execute();

		// Add column for locale context.
		if (db_table_exists('locales_source')) {
			db_add_field('locales_source', 'context', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => '', 'description' => 'The context this string applies to.'));
		}

		// Rename 'site_offline_message' variable to 'maintenance_mode_message'
		// and 'site_offline' variable to 'maintenance_mode'.
		// Old variable is removed in update for system.module, see
		// system_update_7072().
		if ($message = variable_get('site_offline_message', NULL)) {
			variable_set('maintenance_mode_message', $message);
		}
		// Old variable is removed in update for system.module, see
		// system_update_7069().
		$site_offline = variable_get('site_offline', -1);
		if ($site_offline != -1) {
			variable_set('maintenance_mode', $site_offline);
		}

		// Add ssid column and index.
		db_add_field('sessions', 'ssid', array('description' => "Secure session ID. The value is generated by Drupal's session handlers.", 'type' => 'varchar', 'length' => 128, 'not null' => TRUE, 'default' => ''));
		db_add_index('sessions', 'ssid', array('ssid'));
		// Drop existing primary key.
		db_drop_primary_key('sessions');
		// Add new primary key.
		db_add_primary_key('sessions', array('sid', 'ssid'));

		// Allow longer javascript file names.
		if (db_table_exists('languages')) {
			db_change_field('languages', 'javascript', 'javascript', array('type' => 'varchar', 'length' => 64, 'not null' => TRUE, 'default' => ''));
		}

		// Rename action description to label.
		db_change_field('actions', 'description', 'label', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => '0'));

		variable_set('update_d7_requirements', TRUE);
	}

	update_fix_d7_install_profile();
}

/**
 * Register the currently installed profile in the system table.
 *
 * Install profiles are now treated as modules by Drupal, and have an upgrade
 * path based on their schema version in the system table.
 *
 * The install profile will be set to schema_version 0, as it has already been
 * installed. Any other hook_update_N functions provided by the install profile
 * will be run by update.php.
 */
function update_fix_d7_install_profile() {
	$profile = drupal_get_profile();

	$results = db_select('system', 's')
	->fields('s', array('name', 'schema_version'))
	->condition('name', $profile)
	->condition('type', 'module')
	->execute()
	->fetchAll();

	if (empty($results)) {
		$filename = 'profiles/' . $profile . '/' . $profile . '.profile';

		// Read profile info file
		$info = drupal_parse_info_file(dirname($filename) . '/' . $profile . '.info');

		// Merge in defaults.
		$info = $info + array(
				'dependencies' => array(),
				'description' => '',
				'package' => 'Other',
				'version' => NULL,
				'php' => DRUPAL_MINIMUM_PHP,
				'files' => array(),
		);

		// The install profile is always required.
		$file->info['required'] = TRUE;

		$values = array(
				'filename' => $filename,
				'name' => $profile,
				'info' => serialize($info),
				'schema_version' => 0,
				'type' => 'module',
				'status' => 1,
				'owner' => '',
		);

		// Install profile hooks are always executed last by the module system
		$values['weight'] = 1000;

		// Initializing the system table entry for the install profile
		db_insert('system')
		->fields(array_keys($values))
		->values($values)
		->execute();

		// Reset the cached schema version.
		drupal_get_installed_schema_version($profile, TRUE);

		// Load the updates again to make sure the install profile updates are loaded
		drupal_load_updates();
	}
}

/**
 * Parse pre-Drupal 7 database connection URLs and return D7 compatible array.
 *
 * @return
 *   Drupal 7 DBTNG compatible array of database connection information.
 */
function update_parse_db_url($db_url, $db_prefix) {
	$databases = array();
	if (!is_array($db_url)) {
		$db_url = array('default' => $db_url);
	}
	foreach ($db_url as $database => $url) {
		$url = parse_url($url);
		$databases[$database]['default'] = array(
				// MySQLi uses the mysql driver.
				'driver' => $url['scheme'] == 'mysqli' ? 'mysql' : $url['scheme'],
				// Remove the leading slash to get the database name.
				'database' => substr(urldecode($url['path']), 1),
				'username' => urldecode($url['user']),
				'password' => isset($url['pass']) ? urldecode($url['pass']) : '',
				'host' => urldecode($url['host']),
				'port' => isset($url['port']) ? urldecode($url['port']) : '',
		);
		if (isset($db_prefix)) {
			$databases[$database]['default']['prefix'] = $db_prefix;
		}
	}
	return $databases;
}

/**
 * Constructs a session name compatible with a D6 environment.
 *
 * @return
 *   D6-compatible session name string.
 *
 * @see drupal_settings_initialize()
 */
function update_get_d6_session_name() {
	global $base_url, $cookie_domain;
	$cookie_secure = ini_get('session.cookie_secure');

	// If a custom cookie domain is set in settings.php, that variable forms
	// the basis of the session name. Re-compute the D7 hashing method to find
	// out if $cookie_domain was used as the session name.
	if (($cookie_secure ? 'SSESS' : 'SESS') . substr(hash('sha256', $cookie_domain), 0, 32) == session_name()) {
		$session_name = $cookie_domain;
	}
	else {
		// Otherwise use $base_url as session name, without the protocol
		// to use the same session identifiers across http and https.
		list( , $session_name) = explode('://', $base_url, 2);
	}

	if ($cookie_secure) {
		$session_name .= 'SSL';
	}

	return 'SESS' . md5($session_name);
}

/**
 * Perform one update and store the results for display on finished page.
 *
 * If an update function completes successfully, it should return a message
 * as a string indicating success, for example:
 * @code
 * return t('New index added successfully.');
 * @endcode
 *
 * Alternatively, it may return nothing. In that case, no message
 * will be displayed at all.
 *
 * If it fails for whatever reason, it should throw an instance of
 * DrupalUpdateException with an appropriate error message, for example:
 * @code
 * throw new DrupalUpdateException(t('Description of what went wrong'));
 * @endcode
 *
 * If an exception is thrown, the current update and all updates that depend on
 * it will be aborted. The schema version will not be updated in this case, and
 * all the aborted updates will continue to appear on update.php as updates
 * that have not yet been run.
 *
 * If an update function needs to be re-run as part of a batch process, it
 * should accept the $sandbox array by reference as its first parameter
 * and set the #finished property to the percentage completed that it is, as a
 * fraction of 1.
 *
 * @param $module
 *   The module whose update will be run.
 * @param $number
 *   The update number to run.
 * @param $dependency_map
 *   An array whose keys are the names of all update functions that will be
 *   performed during this batch process, and whose values are arrays of other
 *   update functions that each one depends on.
 * @param $context
 *   The batch context array.
 *
 * @see update_resolve_dependencies()
 */
function update_do_one($module, $number, $dependency_map, &$context) {
	$function = $module . '_update_' . $number;

	// If this update was aborted in a previous step, or has a dependency that
	// was aborted in a previous step, go no further.
	if (!empty($context['results']['#abort']) && array_intersect($context['results']['#abort'], array_merge($dependency_map, array($function)))) {
		return;
	}

	$ret = array();
	if (function_exists($function)) {
		try {
			$ret['results']['query'] = $function($context['sandbox']);
			$ret['results']['success'] = TRUE;
		}
		// @TODO We may want to do different error handling for different
		// exception types, but for now we'll just log the exception and
		// return the message for printing.
		catch (Exception $e) {
			watchdog_exception('update', $e);

			require_once DRUPAL_ROOT . '/includes/errors.inc';
			$variables = _drupal_decode_exception($e);
			// The exception message is run through check_plain() by _drupal_decode_exception().
			$ret['#abort'] = array('success' => FALSE, 'query' => t('%type: !message in %function (line %line of %file).', $variables));
		}
	}

	if (isset($context['sandbox']['#finished'])) {
		$context['finished'] = $context['sandbox']['#finished'];
		unset($context['sandbox']['#finished']);
	}

	if (!isset($context['results'][$module])) {
		$context['results'][$module] = array();
	}
	if (!isset($context['results'][$module][$number])) {
		$context['results'][$module][$number] = array();
	}
	$context['results'][$module][$number] = array_merge($context['results'][$module][$number], $ret);

	if (!empty($ret['#abort'])) {
		// Record this function in the list of updates that were aborted.
		$context['results']['#abort'][] = $function;
	}

	// Record the schema update if it was completed successfully.
	if ($context['finished'] == 1 && empty($ret['#abort'])) {
		drupal_set_installed_schema_version($module, $number);
	}

	$context['message'] = 'Updating ' . check_plain($module) . ' module';
}

/**
 * @class Exception class used to throw error if a module update fails.
 */
class DrupalUpdateException extends Exception { }

/**
 * Start the database update batch process.
 *
 * @param $start
 *   An array whose keys contain the names of modules to be updated during the
 *   current batch process, and whose values contain the number of the first
 *   requested update for that module. The actual updates that are run (and the
 *   order they are run in) will depend on the results of passing this data
 *   through the update dependency system.
 * @param $redirect
 *   Path to redirect to when the batch has finished processing.
 * @param $url
 *   URL of the batch processing page (should only be used for separate
 *   scripts like update.php).
 * @param $batch
 *   Optional parameters to pass into the batch API.
 * @param $redirect_callback
 *   (optional) Specify a function to be called to redirect to the progressive
 *   processing page.
 *
 * @see update_resolve_dependencies()
 */
function update_batch($start, $redirect = NULL, $url = NULL, $batch = array(), $redirect_callback = 'drupal_goto') {
	// During the update, bring the site offline so that schema changes do not
	// affect visiting users.
	$_SESSION['maintenance_mode'] = variable_get('maintenance_mode', FALSE);
	if ($_SESSION['maintenance_mode'] == FALSE) {
		variable_set('maintenance_mode', TRUE);
	}

	// Resolve any update dependencies to determine the actual updates that will
	// be run and the order they will be run in.
	$updates = update_resolve_dependencies($start);

	// Store the dependencies for each update function in an array which the
	// batch API can pass in to the batch operation each time it is called. (We
	// do not store the entire update dependency array here because it is
	// potentially very large.)
	$dependency_map = array();
	foreach ($updates as $function => $update) {
		$dependency_map[$function] = !empty($update['reverse_paths']) ? array_keys($update['reverse_paths']) : array();
	}

	$operations = array();
	foreach ($updates as $update) {
		if ($update['allowed']) {
			// Set the installed version of each module so updates will start at the
			// correct place. (The updates are already sorted, so we can simply base
			// this on the first one we come across in the above foreach loop.)
			if (isset($start[$update['module']])) {
				drupal_set_installed_schema_version($update['module'], $update['number'] - 1);
				unset($start[$update['module']]);
			}
			// Add this update function to the batch.
			$function = $update['module'] . '_update_' . $update['number'];
			$operations[] = array('update_do_one', array($update['module'], $update['number'], $dependency_map[$function]));
		}
	}
	$batch['operations'] = $operations;
	$batch += array(
			'title' => 'Updating',
			'init_message' => 'Starting updates',
			'error_message' => 'An unrecoverable error has occurred. You can find the error message below. It is advised to copy it to the clipboard for reference.',
			'finished' => 'update_finished',
			'file' => 'includes/update.inc',
	);
	batch_set($batch);
	batch_process($redirect, $url, $redirect_callback);
}

/**
 * Finish the update process and store results for eventual display.
 *
 * After the updates run, all caches are flushed. The update results are
 * stored into the session (for example, to be displayed on the update results
 * page in update.php). Additionally, if the site was off-line, now that the
 * update process is completed, the site is set back online.
 *
 * @param $success
 *   Indicate that the batch API tasks were all completed successfully.
 * @param $results
 *   An array of all the results that were updated in update_do_one().
 * @param $operations
 *   A list of all the operations that had not been completed by the batch API.
 *
 * @see update_batch()
 */
function update_finished($success, $results, $operations) {
	// Remove the D6 upgrade flag variable so that subsequent update runs do not
	// get the wrong context.
	variable_del('update_d6');

	// Clear the caches in case the data has been updated.
	drupal_flush_all_caches();

	$_SESSION['update_results'] = $results;
	$_SESSION['update_success'] = $success;
	$_SESSION['updates_remaining'] = $operations;

	// Now that the update is done, we can put the site back online if it was
	// previously in maintenance mode.
	if (isset($_SESSION['maintenance_mode']) && $_SESSION['maintenance_mode'] == FALSE) {
		variable_set('maintenance_mode', FALSE);
		unset($_SESSION['maintenance_mode']);
	}
}

/**
 * Return a list of all the pending database updates.
 *
 * @return
 *   An associative array keyed by module name which contains all information
 *   about database updates that need to be run, and any updates that are not
 *   going to proceed due to missing requirements. The system module will
 *   always be listed first.
 *
 *   The subarray for each module can contain the following keys:
 *   - start: The starting update that is to be processed. If this does not
 *       exist then do not process any updates for this module as there are
 *       other requirements that need to be resolved.
 *   - warning: Any warnings about why this module can not be updated.
 *   - pending: An array of all the pending updates for the module including
 *       the update number and the description from source code comment for
 *       each update function. This array is keyed by the update number.
 */
function update_get_update_list() {
	// Make sure that the system module is first in the list of updates.
	$ret = array('system' => array());

	$modules = drupal_get_installed_schema_version(NULL, FALSE, TRUE);
	foreach ($modules as $module => $schema_version) {
		// Skip uninstalled and incompatible modules.
		if ($schema_version == SCHEMA_UNINSTALLED || update_check_incompatibility($module)) {
			continue;
		}
		// Otherwise, get the list of updates defined by this module.
		$updates = drupal_get_schema_versions($module);
		if ($updates !== FALSE) {
			// module_invoke returns NULL for nonexisting hooks, so if no updates
			// are removed, it will == 0.
			$last_removed = module_invoke($module, 'update_last_removed');
			if ($schema_version < $last_removed) {
				$ret[$module]['warning'] = '<em>' . $module . '</em> module can not be updated. Its schema version is ' . $schema_version . '. Updates up to and including ' . $last_removed . ' have been removed in this release. In order to update <em>' . $module . '</em> module, you will first <a href="http://drupal.org/upgrade">need to upgrade</a> to the last version in which these updates were available.';
				continue;
			}

			$updates = drupal_map_assoc($updates);
			foreach (array_keys($updates) as $update) {
				if ($update > $schema_version) {
					// The description for an update comes from its Doxygen.
					$func = new ReflectionFunction($module . '_update_' . $update);
					$description = str_replace(array("\n", '*', '/'), '', $func->getDocComment());
					$ret[$module]['pending'][$update] = "$update - $description";
					if (!isset($ret[$module]['start'])) {
						$ret[$module]['start'] = $update;
					}
				}
			}
			if (!isset($ret[$module]['start']) && isset($ret[$module]['pending'])) {
				$ret[$module]['start'] = $schema_version;
			}
		}
	}

	if (empty($ret['system'])) {
		unset($ret['system']);
	}
	return $ret;
}

/**
 * Resolves dependencies in a set of module updates, and orders them correctly.
 *
 * This function receives a list of requested module updates and determines an
 * appropriate order to run them in such that all update dependencies are met.
 * Any updates whose dependencies cannot be met are included in the returned
 * array but have the key 'allowed' set to FALSE; the calling function should
 * take responsibility for ensuring that these updates are ultimately not
 * performed.
 *
 * In addition, the returned array also includes detailed information about the
 * dependency chain for each update, as provided by the depth-first search
 * algorithm in drupal_depth_first_search().
 *
 * @param $starting_updates
 *   An array whose keys contain the names of modules with updates to be run
 *   and whose values contain the number of the first requested update for that
 *   module.
 *
 * @return
 *   An array whose keys are the names of all update functions within the
 *   provided modules that would need to be run in order to fulfill the
 *   request, arranged in the order in which the update functions should be
 *   run. (This includes the provided starting update for each module and all
 *   subsequent updates that are available.) The values are themselves arrays
 *   containing all the keys provided by the drupal_depth_first_search()
 *   algorithm, which encode detailed information about the dependency chain
 *   for this update function (for example: 'paths', 'reverse_paths', 'weight',
 *   and 'component'), as well as the following additional keys:
 *   - 'allowed': A boolean which is TRUE when the update function's
 *     dependencies are met, and FALSE otherwise. Calling functions should
 *     inspect this value before running the update.
 *   - 'missing_dependencies': An array containing the names of any other
 *     update functions that are required by this one but that are unavailable
 *     to be run. This array will be empty when 'allowed' is TRUE.
 *   - 'module': The name of the module that this update function belongs to.
 *   - 'number': The number of this update function within that module.
 *
 * @see drupal_depth_first_search()
 */
function update_resolve_dependencies($starting_updates) {
	// Obtain a dependency graph for the requested update functions.
	$update_functions = update_get_update_function_list($starting_updates);
	$graph = update_build_dependency_graph($update_functions);

	// Perform the depth-first search and sort the results.
	require_once DRUPAL_ROOT . '/includes/graph.inc';
	drupal_depth_first_search($graph);
	uasort($graph, 'drupal_sort_weight');

	foreach ($graph as $function => &$data) {
		$module = $data['module'];
		$number = $data['number'];
		// If the update function is missing and has not yet been performed, mark
		// it and everything that ultimately depends on it as disallowed.
		if (update_is_missing($module, $number, $update_functions) && !update_already_performed($module, $number)) {
			$data['allowed'] = FALSE;
			foreach (array_keys($data['paths']) as $dependent) {
				$graph[$dependent]['allowed'] = FALSE;
				$graph[$dependent]['missing_dependencies'][] = $function;
			}
		}
		elseif (!isset($data['allowed'])) {
			$data['allowed'] = TRUE;
			$data['missing_dependencies'] = array();
		}
		// Now that we have finished processing this function, remove it from the
		// graph if it was not part of the original list. This ensures that we
		// never try to run any updates that were not specifically requested.
		if (!isset($update_functions[$module][$number])) {
			unset($graph[$function]);
		}
	}

	return $graph;
}

/**
 * Returns an organized list of update functions for a set of modules.
 *
 * @param $starting_updates
 *   An array whose keys contain the names of modules and whose values contain
 *   the number of the first requested update for that module.
 *
 * @return
 *   An array containing all the update functions that should be run for each
 *   module, including the provided starting update and all subsequent updates
 *   that are available. The keys of the array contain the module names, and
 *   each value is an ordered array of update functions, keyed by the update
 *   number.
 *
 * @see update_resolve_dependencies()
 */
function update_get_update_function_list($starting_updates) {
	// Go through each module and find all updates that we need (including the
	// first update that was requested and any updates that run after it).
	$update_functions = array();
	foreach ($starting_updates as $module => $version) {
		$update_functions[$module] = array();
		$updates = drupal_get_schema_versions($module);
		if ($updates !== FALSE) {
			$max_version = max($updates);
			if ($version <= $max_version) {
				foreach ($updates as $update) {
					if ($update >= $version) {
						$update_functions[$module][$update] = $module . '_update_' . $update;
					}
				}
			}
		}
	}
	return $update_functions;
}

/**
 * Constructs a graph which encodes the dependencies between module updates.
 *
 * This function returns an associative array which contains a "directed graph"
 * representation of the dependencies between a provided list of update
 * functions, as well as any outside update functions that they directly depend
 * on but that were not in the provided list. The vertices of the graph
 * represent the update functions themselves, and each edge represents a
 * requirement that the first update function needs to run before the second.
 * For example, consider this graph:
 *
 * system_update_7000 ---> system_update_7001 ---> system_update_7002
 *
 * Visually, this indicates that system_update_7000() must run before
 * system_update_7001(), which in turn must run before system_update_7002().
 *
 * The function takes into account standard dependencies within each module, as
 * shown above (i.e., the fact that each module's updates must run in numerical
 * order), but also finds any cross-module dependencies that are defined by
 * modules which implement hook_update_dependencies(), and builds them into the
 * graph as well.
 *
 * @param $update_functions
 *   An organized array of update functions, in the format returned by
 *   update_get_update_function_list().
 *
 * @return
 *   A multidimensional array representing the dependency graph, suitable for
 *   passing in to drupal_depth_first_search(), but with extra information
 *   about each update function also included. Each array key contains the name
 *   of an update function, including all update functions from the provided
 *   list as well as any outside update functions which they directly depend
 *   on. Each value is an associative array containing the following keys:
 *   - 'edges': A representation of any other update functions that immediately
 *     depend on this one. See drupal_depth_first_search() for more details on
 *     the format.
 *   - 'module': The name of the module that this update function belongs to.
 *   - 'number': The number of this update function within that module.
 *
 * @see drupal_depth_first_search()
 * @see update_resolve_dependencies()
 */
function update_build_dependency_graph($update_functions) {
	// Initialize an array that will define a directed graph representing the
	// dependencies between update functions.
	$graph = array();

	// Go through each update function and build an initial list of dependencies.
	foreach ($update_functions as $module => $functions) {
		$previous_function = NULL;
		foreach ($functions as $number => $function) {
			// Add an edge to the directed graph representing the fact that each
			// update function in a given module must run after the update that
			// numerically precedes it.
			if ($previous_function) {
				$graph[$previous_function]['edges'][$function] = TRUE;
			}
			$previous_function = $function;

			// Define the module and update number associated with this function.
			$graph[$function]['module'] = $module;
			$graph[$function]['number'] = $number;
		}
	}

	// Now add any explicit update dependencies declared by modules.
	$update_dependencies = update_retrieve_dependencies();
	foreach ($graph as $function => $data) {
		if (!empty($update_dependencies[$data['module']][$data['number']])) {
			foreach ($update_dependencies[$data['module']][$data['number']] as $module => $number) {
				$dependency = $module . '_update_' . $number;
				$graph[$dependency]['edges'][$function] = TRUE;
				$graph[$dependency]['module'] = $module;
				$graph[$dependency]['number'] = $number;
			}
		}
	}

	return $graph;
}

/**
 * Determines if a module update is missing or unavailable.
 *
 * @param $module
 *   The name of the module.
 * @param $number
 *   The number of the update within that module.
 * @param $update_functions
 *   An organized array of update functions, in the format returned by
 *   update_get_update_function_list(). This should represent all module
 *   updates that are requested to run at the time this function is called.
 *
 * @return
 *   TRUE if the provided module update is not installed or is not in the
 *   provided list of updates to run; FALSE otherwise.
 */
function update_is_missing($module, $number, $update_functions) {
	return !isset($update_functions[$module][$number]) || !function_exists($update_functions[$module][$number]);
}

/**
 * Determines if a module update has already been performed.
 *
 * @param $module
 *   The name of the module.
 * @param $number
 *   The number of the update within that module.
 *
 * @return
 *   TRUE if the database schema indicates that the update has already been
 *   performed; FALSE otherwise.
 */
function update_already_performed($module, $number) {
	return $number <= drupal_get_installed_schema_version($module);
}

/**
 * Invoke hook_update_dependencies() in all installed modules.
 *
 * This function is similar to module_invoke_all(), with the main difference
 * that it does not require that a module be enabled to invoke its hook, only
 * that it be installed. This allows the update system to properly perform
 * updates even on modules that are currently disabled.
 *
 * @return
 *   An array of return values obtained by merging the results of the
 *   hook_update_dependencies() implementations in all installed modules.
 *
 * @see module_invoke_all()
 * @see hook_update_dependencies()
 */
function update_retrieve_dependencies() {
	$return = array();
	// Get a list of installed modules, arranged so that we invoke their hooks in
	// the same order that module_invoke_all() does.
	$modules = db_query("SELECT name FROM {system} WHERE type = 'module' AND schema_version <> :schema ORDER BY weight ASC, name ASC", array(':schema' => SCHEMA_UNINSTALLED))->fetchCol();
	foreach ($modules as $module) {
		$function = $module . '_update_dependencies';
		if (function_exists($function)) {
			$result = $function();
			// Each implementation of hook_update_dependencies() returns a
			// multidimensional, associative array containing some keys that
			// represent module names (which are strings) and other keys that
			// represent update function numbers (which are integers). We cannot use
			// array_merge_recursive() to properly merge these results, since it
			// treats strings and integers differently. Therefore, we have to
			// explicitly loop through the expected array structure here and perform
			// the merge manually.
			if (isset($result) && is_array($result)) {
				foreach ($result as $module => $module_data) {
					foreach ($module_data as $update => $update_data) {
						foreach ($update_data as $module_dependency => $update_dependency) {
							// If there are redundant dependencies declared for the same
							// update function (so that it is declared to depend on more than
							// one update from a particular module), record the dependency on
							// the highest numbered update here, since that automatically
							// implies the previous ones. For example, if one module's
							// implementation of hook_update_dependencies() required this
							// ordering:
							//
							// system_update_7001 ---> user_update_7000
							//
							// but another module's implementation of the hook required this
							// one:
							//
							// system_update_7002 ---> user_update_7000
							//
							// we record the second one, since system_update_7001() is always
							// guaranteed to run before system_update_7002() anyway (within
							// an individual module, updates are always run in numerical
							// order).
							if (!isset($return[$module][$update][$module_dependency]) || $update_dependency > $return[$module][$update][$module_dependency]) {
								$return[$module][$update][$module_dependency] = $update_dependency;
							}
						}
					}
				}
			}
		}
	}

	return $return;
}

/**
 * @defgroup update-api-6.x-to-7.x Update versions of API functions
 * @{
 * Functions similar to normal API function but not firing hooks.
 *
 * During update, it is impossible to judge the consequences of firing a hook
 * as it might hit a module not yet updated. So simplified versions of some
 * core APIs are provided.
 */

/**
 * @} End of "defgroup update-api-6.x-to-7.x"
 */
